Getting specific values from 3D matrix

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Dylan George 2019-1-9

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评论： Dylan George 2019-1-10

Hi all, I have a 1200x1200x100 matrix and I'm trying to select/crop it using x indicies and y indicies I have found of interest. The all 4 lists of coordinates are 1x34 matrix. I should be getting something like 150x160x100 but running into problems using loops. Thank you for any help!

for N=1:34
xdata(N) = data(X1coordinates(N):X2coordinates(N),Y1coordinates(N):Y2coordinates(N),100);
end

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Bob Thompson 2019-1-9

What do you mean by "it only works for the first row."?

Dylan George 2019-1-10

The first row - meaning x1coordinates(1,1) :coordinates(1,1) and y1coordinates(1,1):y2coordinates(1,1) . Not all 34 rows which I need.

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Guillaume 2019-1-10

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If the areas are different sizes, then you don't have a choice but storing them in a cell array. The code you have written is the correct approach. I suspect that it only works for the first row because your X1Coordinates is a column vector whereas your code assumes it's a row vector. That's easily fixed by iterating over the rows instead of columns or even better, by writing code that makes no assumption about the shape of the inputs and simply iterate over all the elements:

xdata = cell(size(X1coordinates));  %result is same shape and number of elements as X1coordinates
for i = 1 : numel(xdata)   %iterate over all the elements
    xdata{i} = data(X1coordinates{i}:X2coordinates{i}, Y1coordinates{i}:Y2coordinates{i}, :);
end

Or you can replace the whole lot by a single arrayfun:

xdata = arrayfun(@(x1, x2, y1, y2) data(x1:x2, y1:y2, :), X1coordinates, X2coordinates, Y1coordinates, Y2coordinates, 'UniformOutput', false);

Note that if your original code is correct, the name Xncoordinates, and Yncoordinates are a bit misleading, since your X is along the rows and Y along the columns which is not the standard convention.